Hello.
Firstly, for the client-side, as Android is based on a linux kernel, you might be able to play using a Play On Linux solution, as we usually do on mac using Wine. But I am not sure that a linux software would run "as is" on Android.
If you plan to distribute your own game client on Android, firstly, for copyright issues you won't be able to put it in Google Play.
Then, you won't even be able to share an .apk, as if you succeed in making an Android game client with Play On Linux or something like that, you'll proably need a root access if its not a complete new OS forked from original Android.
Then for server-side... I simply can't see the goal of that.
What I suggest you :
For client side, you could try making a "cloud based streaming" app. User would simply send his input to a server, and the server would return a video. It is doable.
But:
* 1: Player would need need optical Fiber or 4G+ (if not 5G)
* 2: You'll face lags, with might be not ideal for a PVP Game
* 3: You'll need to code a lot things... For very few players, as very few people have a decent internet.
* 4: You'll need server-side GPU, and sadly GPU are not cheap at all. And Shaiya is a poorly optimized game, so it would be very expensive, for very few gains : DONT DO THAT.
Alternative way :
* You can try using Ubuntu Touch, which is sadly a dead project. If you find a "true" linux OS for mobile, then as I told you above, your players would obviously have to install this OS, and it won't be android at all.
For server side I would suggest you to use linux : you can try running server-files with Play On Linux or something equivalent, for SQL Server, it is now available on linux since 2017 version. But you'll probably face lot of issues with server-files.
Staying on windows is a better idea for now in my opinion. If you want to code a such thing, you should seriously consider creating a new game, it would require the same code quantity, and you will not face obvious legal issues.